Modeling and FEM-Based Simulations of Composite Membrane Based Circular Capacitive Pressure Sensor

Abstract

In Micro-electro-mechanical Systems (MEMS) based pressure sensors and acoustic devices, deflection of a membrane is utilized for pressure or sound measurements. Due to advantages of capacitive pressure sensor over piezoresistive pressure sensors (low power consumption, less sensitive to temperature drift, higher dynamic range, high sensitivity), capacitive pressure sensors are the 2nd largest useable MEMS-based sensor after piezoresistive pressure sensors. We present a normal capacitive pressure sensor, for continuous sensing of normal and abnormal Intraocular Pressure (IOP). The composite membrane of the sensor is made of three materials, i.e., Si, SiO 2 and Si 3 N 4 . The membrane deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity and non-linearity are discussed in this work. Mathematical modeling is performed for analytical simulation, which is also compared with Finite Element Method (FEM) simulations. MATLAB ® is used for analytical simulations and CoventorWare ® is used for FEM simulations. The variation in analytical result of deflection in membrane w.r.t. FEM result is about 7.19%, and for capacitance, the variation is about 2.7% at maximum pressure of 8 kPa. The nonlinearity is about 4.2492% for the proposed sensor for fabrication using surface micro-machining process.

Mathematical Modelling and Comparative Study of Elliptical and Circular Capacitive Pressure Microsensor

“…In case of zero eccentricity i.e. for the circular diaphragm (when a = b = L), the capacitance after pressure application can be given by [4,[7][8][9]:…”

“…pressure range. Then capacitive sensitivity of elliptical shaped capacitive pressure sensor can be given by [8][9]:…”

“…Some issues must be addressed by circuitry which is used to measure the change in capacitance. As sealing the vacuum cavity is complex task, so proper care must be been taken at the time of fabrication and packaging the absolute capacitive pressure sensor [7][8][9].…”

Polymer/paper-based double touch mode capacitive pressure sensing element for wireless control of robotic arm

“…Among MEMS pressure sensor's arena, capacitive pressure sensors have several advantages like low temperature drift, high sensitivity, simple structure, low power consumption and lower sensitivity to stress at the edges of the mechanical sensitive element which will deform/deflect after pressure application [5][6][25][26]. However, the nonlinearity between capacitance change versus applied pressure and effect of stray capacitance are major issues when the pressure sensor is operating in the normal mode [21][22].…”

“…Touch-mode pressure sensors offer high pressure range, linear response and high overload protection. However, touch mode capacitive pressure sensors have disproportionate relationship between capacitance change v/s applied pressure and a short linear region which causes the sensor to reach saturation mode very fast [25][26]31]. Thus, continuous efforts have been made to develop approaches aimed at enhancing the linearity region and proportionality of capacitance variation with respect to applied pressure such as double side diaphragm touch mode [32][33], island structure sensor [34], sandwich diaphragm [35] and double touch mode [28,37] capacitive pressure sensors.…”